Something is puzzling me about the use of ftp.nlst on a windows ftp server - ruby

Question

So I was reading the documentation for the method nlst in the NET::FTP module (ruby-1.8.6). The source code displayed is
# File net/ftp.rb, line 602
def nlst(dir = nil)
cmd = "NLST"
if dir
cmd = cmd + " " + dir
end
files = []
retrlines(cmd) do |line|
files.push(line)
end
return files
end
So the command is written literally in the string cmd, executed via retrlines and the list of files is given back right?
The thing I don't understand is that on my windows ftp server there is no such command:
230 User logged in.
Remote system type is Windows_NT.
ftp> nlst
?Invalid command
ftp>
and yet the the method returns the file list. How is it possible? The source code doesn't appear to have an abstraction of some sort on the command and also the source code of retrlines doesn't have anything special (to me).
# File lib/net/ftp.rb, line 475
def retrlines(cmd) # :yield: line
synchronize do
with_binary(false) do
conn = transfercmd(cmd)
loop do
line = conn.gets
break if line == nil
yield(line.sub(/\r?\n\z/, ""), !line.match(/\n\z/).nil?)
end
conn.close
voidresp
end
end
end
I traced back the methods called to sendcmd inside transfercmd but I have no clue really.

Answer 1

The question is who is telling you ?Invalid command?
In this case it's the FTP client, not the server.
The client is just a front-end for commands that it implements, converting these front-end commands into proper FTP protocol command strings for the server.
What you're looking for is the nlist (not nlst) command in your client, which will issue the NLST FTP protocol command to the server.
ftp> help nlst
?Invalid help command nlst
ftp> help nlist
nlist nlist contents of remote directory
ftp>